CS247155B2 - Fine powder silicon dioxide production method - Google Patents

Abstract

1. Finely-divided silica which is, at the same time, suitable as a filtration auxiliary and as a beer stabilizer in the filtration of beer, characterised in that it is obtained by gradually adding waterglass and acid separately to an aqueous starting solution which contains dissolved sodium chloride in an amount of from 0.4 to 2% by weight, the volume of the starting solution being from at least 33%, by volume to at most 70% by volume, of the final volume on completion of precipitation, the metering operation being adjusted so that, during addition to the starting solution, the pH is from 3 to 10 and the temperature is from 50 to 95 degrees C, the silica suspension is adjusted to a pH of from 7 to 4 on completion of addition, the resulting silica is filtered, the resulting filter cake is washed with water and is immediately dried while avoiding substantial shearing forces and the mass is sieved after drying using a sieving apparatus, and silica particles are thereby obtained having a substantially spherical or rotationally ellipsoidal form, a minimum SiO2 content of 95% by weight, on a dry solids basis at about 100 degrees C, an Na2 O content of less than 0.25% by weight, a pH, measured on a 10% suspension in water, of from 4 to 7, a maximum Carman surface area of 100 m**2 /g, a standard test filtration time t0 , as defined in the following, of from 20 sec to 6 min and a ratio t120-1000 /t0 of from 0.7 to 6.5, wherein t120-1000 represents the test filtration time after stir stressing for 120 min at 1000 rpm, the stirring stress being determined by pouring 2 liters of water and 40 g of filtration auxiliary into a 2-litre measuring vessel which is 16 cm in height, has a bottom diameter of 12 cm and a top diameter of 14 cm, and lowering a stirring device having 4 blades 2 cm in length, which are inclined downwardly with respect to the horizontal at an angle of 25 degrees C, into the vessel to a depth of immersion of 8 cm and allowing it to rotate for 120 min at a constant speed of 1000 rpm.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of wet-precipitated, artificially produced, finely divided silica which is also suitable as a filter aid and as a stabilizing agent for beer in its filtration. ·

Fine-powdered silica of natural origin and also fine-powdered silica produced synthetically have long been known.

Silicon dioxide is used in many industries, such as fillers of natural and synthetic rubber, as pigment in coatings, in the manufacture of pharmaceutical or cosmetic powders, or as a substrate for. catalysts, and also in the production of beer as a filter aid or stabilizer, as described, for example, in DD 54 671 and in a paper by Clark et al. The use of silica hydrogel for combined filtration and stabilization, published in The Brewer, June 1980, pp. 168-171.

Since silica with a certain set of properties is desirable for each particular field of application due to different requirements and since certain features of one silica may be advantageous for one purpose but very disadvantageous for another purpose, it is clear that, for example, silica cannot be used. , which is a good filler for the elastomers, as a filter aid or as a stabilizing agent in beer production.

For this reason, the known production methods always lead only to silicas which can advantageously be used for a completely specific field of application.

The known wet-precipitated synthetic silicas used as fillers have a number of disadvantages due to their use for beer filtration. They are too finely powdered in the original state, and their mechanical stability is not sufficient, so that, for example, filtration with alluvial metering devices such as pumps and agitators, especially when using rotary pumps, breaks down the silica grains into even finer particles, so after a short time clog.

If, in the flow-through contact process, the beer without filter aid is also to be free of turbidity by filtering the hydrogels and stabilized by protein adsorption, there is a risk that the protein adsorption becomes too high, so that the hydrogel acts both as filter aid and adsorbent , is adsorbed by the adsorbed proteins and haze-causing substances, and after a short time, a very large pressure difference occurs at the inlet and outlet side of the filter and clogs rapidly. In addition, the quality of the beer is negatively affected by the excessive adsorption of proteins.

Although a number of filter kieselguhr and several synthetically produced silica which can be used for beer filtration are already known, there is still a need for improved synthetically produced silica which does not exhibit the above drawbacks.

SUMMARY OF THE INVENTION The object of the present invention is to provide a wet-precipitated synthetic fine-powdered silica which enables simultaneous filtration of beer and its stabilization against cold in the contact flow process, without overly burdening the filter aid with excessive protein adsorption and adversely affecting beer quality. especially its taste, foam formation and its durability.

It is a further object of the invention to provide a silica having a mechanically stable structure, a favorable grain distribution, a good fining ability and a -2-1 high power in hl and a complete or at least very far-reaching replacement of filter diatomaceous earth.

The above-mentioned drawbacks do not have the process for the production of the finely divided silica according to the invention, which consists in adding to an aqueous template having a volume of 33 to 70% of the final volume after precipitation and containing dissolved sodium chloride at a weight concentration of 0.4 to 2%, uniformly and separately added to the waterglass solution and the acid, wherein the dosage is controlled so that the pH value in the receiver is maintained during the addition in a range ^{from 3 to 10} and ^t ep ^l OTA ^r ozmez ^{at 50 and 25} ° ^C, along with ^the online ^{learning Add} Avan ^{í p} H dioxide slurry to ^row phosphosilicate adjusted to 7-4, the obtained oxide, silica is filtered, the resulting filter cake washed with water and immediately dried, taking care to avoid shear forces to the resulting product, and after drying, the mass is sieved by means of an extruder.

Preferably, the volume of the original is at least 50% of the final volume after the precipitation. Sulfuric acid is very suitable as a precipitation acid. Brush extrusion screens can be used for screening. It is preferred that the screens used have a mesh size in the range of 1 to 2 mm.

The silica obtained by the process of the invention comprises spherical or rotationally ellipsoidal particles having a silica content of at least 25% by weight based on the dry weight obtained by drying at 110 ° C, with a sodium oxide content of at most 0.25% by weight, with a pH value measured in a 10% suspension, in the range of 4 to 7, with a surface according _to -1

Carmana at most 100 m. g, ^d in the ^LSI and to define ^and m ^is in the range from 0.7 to 6.5, where ^J 0 is ⁰⁰ at 1000 rpm.

with the duration of the filtration T _Q in the standard assay as ^{20 to} und ^{t o h} 6 minutes and the ratio ^of the note ^d ru ^ ^^ 0 20 ^extended between ^the duration of filtration test after stirring period of 120 minutes

Preferably, the finely divided silica has a SiO2 content of at least 22% by weight. ^J e ^{d h} o above ^{No, d} YZ ^p value om ^e r ^^ θ ⁰ / ^ is in the range ^{of approx} izn is ^from 1 to ^{the fourth} The ^{l i} m ⁱ Pr ^I zn V ^e, the length of time during the filtration test, f _"1 ^Zt ^ 120 ^ °° is at most 10 minutes.

Finely powdered oxide surface 2 - 1 g ² . g ¹ . The preferred length of time, i.e., silica, is in the range of approximately Carman based silica, preferably at most filtration in a standard fine-powder test of 30 to 150 seconds.

The preferred surface area (BET) of the finely divided silica is in the range of about 15

1 · 2 -1 to 350 m. g, in particular in the range of 40 to 60 m. g. In a particularly preferred embodiment of the invention, the silica particle size distribution determined by wet sieve analysis using Seitz ultrasonic sieves has a residue of at least 60% at 40 µm, a residue of about 15 to 30% at 15 µm, and a residue of about 1 to 5% with a mesh size of 5 µm and a solids content of less than 5 µm and a maximum of 5%.

An extrusion device is a device known as an auxiliary sieve device which serves to extrude or tolerate or disintegrate the respective products. Suitable extrusion devices are described, for example, in the gen / Wurttenberg prospectus Swinging sulfur machines, page 3, prospectus no. AVA

Allgaier-Werke GmbH, Uhrin4 510/3 000 D.

The attached figure shows a filter device for measuring the filtration time.

The duration of filtration in a standard test is determined according to the method described below. ProSeitz, o pass-through, measuring line requires, for example: • single-layer Seitz-Filterwerke Theo and Geo Bad Kreuznach, compressed air, 15 cm pressure gauge by Macharei and Nagel, two-liter fine-gauge, Mn 615 filter paper or paper of the same quality, 2 liter graduated cylinder and shank.

is described with respect to the vertical position and is preferably an attached figure. For measurement, the filter is mounted on a rack. Lower part 2 of the filter device of the device

The procedure placed in can be loosened by loosening the six tilt screws 2, then filter paper is inserted into the removed bottom 2 so that the smooth side of the paper faces the sieve plate and the sieve side of the paper (rough side) faces up. '

Then the filtering device is screwed in such a way that the two opposite wing nuts are always tightened.

247155 4 simultaneously and evenly. After filling and closing, the filter device can be maintained at a constant overpressure of 0.05 MPa through a gas valve 6 by means of compressed air from a steel bottle or a compressor with a pressure reducing valve and a pressure gauge.

The overpressure is adjusted to 0.05 MPa first with the gas valve 6 closed. In a 2 liter volumetric beaker, with stirring by a glass rod, 40 g of filter aid is dissolved in 2 liters of tap water and the resulting suspension is poured through the filling opening 6 into the infusion space 2 with the gas tap open 6.

The filling opening 8 and the gas tap 7 are then closed. When the gas tap 6 is opened, the pressure in the filter device is increased to the indicated value and at the same time the shank is started. During filtration, the pressure must be kept constant at a pressure of 0.05 MPa overpressure.

In the event that the pressure starts to fluctuate, this fluctuation must be compensated by additional regulation on the pressure reducing valve. Prior to filtration, the filtrate effluent becomes irregular. Shortly after it is clearly heard, gas starts to flow out of the drain.

At this point it is necessary to stop the stopwatch. Subtracted time represents the time duration T _Q filter in a standard test. In the accompanying drawing, the reference numeral 6 denotes the outlet of the filter device and the reference numeral 8 denotes the safety valve.

Ho note ^d ratio ^{of t} ru ^{| 2} Q ⁰ / ^t o ^E i ^ řkkem hundred ^trillion IT ^y auxiliary ^eh by ^fil t.račn ^¹H O ^P ros e ^{tr dk} ua reflects the extent to which the filter medium during filtration changing shear forces. The duration of the filtration at the test is determined by the same procedure and in the same measuring device as the duration of the filtration at the standard test.

Unlike the determination of _Q t, wherein the diatomaceous earth or silicas investigated in the condition in which they are delivered, in determining the duration of the filtration T ^^ ⁰⁰ is suspended 40 g of kieselguhr supplied optionally filter aid in 2 liters of water and then subjected to a shear load of 120 minutes using a stirrer rotating at 1000 rpm.

^Liz e ^y values Ο ^ θθθ in ^E t ^width than t _Q u ^to azuje that b ^EH em ^{us, and} HAN ^s contractile forces the silica particles further pulverized, so that the grains of filter aid become even finer .

If the duration of the filtration T ^ g of less than ⁰⁰ t _Q shows that smaller particles are clustered in larger or the smaller particles adsorbed on larger.

The shear forces for determining the value ^{shall be} adjusted as follows:

A 2 liter volumetric beaker of 16 cm height, 12 cm lower diameter and 14 cm upper diameter was charged with 2 liters of water and 40 g of filter aid. To the flask to a depth of immersion of 8 cm stirrer ^{l of manufacture} of the blades ^{4 and} a length of ^{2 to} Cn ^ ter ^{E KL} on n ^{g e s} down Uh ^ ² 5 ° with respect to, a horizontal plane; The stirrer is allowed to run for 120 minutes at a constant speed of 1000 rpm. Immediately followed by filtration.

The determination of the grain size distribution according to Seitz is described in more detail in a paper by Schoffel and Scháfer Versuche zur Charakterisierung von Kieselguren in Brauwelt Magazine No. 18 (1980). In this process, thin sheets are used as a sieve, in which rectangular holes of 5, 15 and 8 mm respectively are galvanically formed. 40

Such sieves can be more accurately determined than with woven sieves which are characterized by significantly greater statistical mesh size variation.

The process for producing the finely divided silica according to the invention can be carried out, for example, as follows:

First, a pattern is made by dissolving sodium chloride in water. The water should be at least of drinking water quality. Sodium chloride should have a weight concentration in the range of about 0.4 to at most 2%. The volume of the template is at least 33%, preferably at least 50% to at most 70% of the final volume that is achieved after all addition of the waterglass and acid solution is complete.

By varying the size of the pattern, the surface area of the silica obtained can be controlled. Generally, by increasing the volume of the artwork at the same amount of salt, i.e., at the same time the initial concentration of sodium chloride decreases, the silica surface will increase; an increase in sodium chloride concentration with an equally large pattern leads to coarser grain and smaller BET and Carman surfaces.

Value

This value is in the

The pH of the sample should be within the range of from 3 to 10, preferably from 5 to 10, at the beginning of the dosage, during the separate addition of the waterglass and acid solution, especially within the preferred limits.

^g re U ^L U is such that ^{the d} and ranges ^{from 50} to ⁹⁵ ° C. After stončení ^{There are} added to the value of ^P is the pH lota, if not already in this range, adjusted to about 7 to 4

Filtration of the diluted silica slurry together with said solids content in the filter cake, which is preferably performed in filter presses. In this way, the precipitation conditions reach a relatively high level and are advantageous in subsequent drying.

in the usual way with water. The solids content of the filtered silica was washed with a rotary cake of approximately 25 to 50%. The filtered silica is then immediately dried. When drying, it must be ensured that it takes place without much shearing stress.

Stronger shear forces can arise, for example, by conveying the material by screw conveyors or by subjecting it to other stronger mechanical forces before drying. Preferably, the silica is conveyed directly from the filter press to the conveyor belt and fed to the conveyor belt for drying.

Advantageously, when using conveyor belts which can pass through the dryer, drying occurs

So it is to the forces as they can directly on the conveyor belt. In this way, it is possible to avoid further deformation, for example due to the inherent pressure and shocks during intermediate storage.

is passed to the sieving after leaving the dryer. It uses a screen which operates in the form of extrusion screens. A brush screening machine is particularly preferred.

Dried material

It is surprising that the silicas thus produced can be sieved without difficulty and pass through the sieve in the desired fineness and grain distribution without the need to grind the dried material.

Yippee

A conventional waterglass solution having a concentration of, for example, 8 to 10% may be used for dosing. An acid, preferably sulfuric acid, is used to neutralize or precipitate. preferably, the acid has a concentration of 2 to 6 N.

During the addition of the waterglass solution and the acid, approximately 95% of the total amount of waterglass solution is added to the reaction solution, then the pH is added to the remaining 5% waterglass by adding the remaining amount of acid.

Preferably, the mixture is stirred. Preferably, the acids are, for example, 4 or about 2 hours, and then

After the addition is complete, the reaction mixture may be filtered immediately with a suspension.

stirring, for example 15 to 30 minutes.

The concentration of silica, calculated as SiO 2, in the final volume of the suspension may vary within relatively wide limits; preferred concentrations are, for example, 70 to 95 g SiO ₂ per liter.

Conventional filter presses are suitable for filtration.

It is particularly surprising that according to the invention it is possible to produce finely powdered silicas which can be used as filter aids as well as stabilizing agents during beer filtration, especially since to date knowledge 2-1 requires surfaces for adsorption of proteins. range 350 to 800 m. g and high fineness of grinding, i.e. at least 99% of the particles should have a diameter of at most 40 µm.

The desired grain size distribution is achieved by the aforementioned precipitation conditions and simple sieving of the dried mass; there is no need to grind the dried mass and it is usually undesirable.

The silica produced by the process of the present invention can be treated together with diatomaceous earth, and is additionally particularly useful. suitable for the total or partial replacement of coarse to medium fine kieselguhr. Compared to diatomaceous earth, the silica produced by the process according to the invention also has the advantage that it can be produced in an unchanging quality, that it does not contain iron or any crystalline components harmful to the lungs, such as quartz, and does not have kieselguhr, various characteristics, varying from place of origin and delivery.

The silica produced by the process of the invention is mechanically very stable; it can be used without any problems both during the first and second wash as well as for dosing. Due to its excellent surface texture, this material is characterized by very good fining and filtering performance and is therefore well suited for beer filtration and its simultaneous stabilization in the contact flow process. There is no undesirable adsorption of the substances contained in the beer.

The silica produced by the process of the invention allows a high filter life; the texture of the filter cake is excellent and the volume of grain space is very favorable, important for the fining ability and filter life.

The invention is illustrated by the following examples.

Example 1

160 g of sodium chloride are dissolved in the present 8 liters of tap water and the solution is heated to 60 ° C. With stirring at pH 10 separately over 2 hours was added 3.75L of water glass having a weight concentration of 27% SiO ₂ and a molar ratio Na ₂ 0: SiO ₂ = 1: 3.3, and dilute sulfuric acid (prepared from 417 ml 95% sulfuric acid and 2.09 liters of water).

The pH is adjusted to a final value of 5 by adding approximately 100 ml of the same dilute sulfuric acid. The stirring time to maintain a constant pH of 5 takes approximately 15 minutes. The reaction mixture was filtered and the filter cake was washed with water.

The solids content by weight of the nuclide is 35.2%. The product, conveyed and dried to avoid shear, contains 0.5% by weight of the total amount of ions, i.e. sodium, chloride and sulfate, contained in the water.

-1 2 —1

Carman's surface is 31 m. g, BET surface is 232 m. g. The filtration time t is 85 seconds and 2 ₂ θ ⁰⁰ = 332 seconds. Hence the value of the ratio ^ οθθ ^ ο ^{= 3} '73 ^,

Example 2

Similarly, using the present 8 liters of water and 80 g of sodium chloride, silica is obtained by precipitation at pH 8 over 2 hours using sulfuric acid prepared by mixing 400 ml of 95% sulfuric acid with 3.2 liters of water and 3.8 liters of water. Glass (graded in the example)

1). The solids content was 37.8%, the Carman surface was 27 m, the content of ions, i.e. sodium, chloride, in the water was _Q t = 34 seconds and t = 0 ⁰⁰ = 1776 seconds, 2020 ° C = 5.18.

-1 2-1. g, BET surface 57 m. g, and the sulfate ions, is 0.1%;

Example 3 (comparative example)

Proceeding as salts precipitate as per ^t l and ² of °° ^{amounts to 990} und.

in Example 2, but using 80 g of sulfuric acid, whose anhydrous sodium sulfate t is 91 seconds.

Claims (2)

1. A process for the production of fine-powdered oxide having a volume of 33 to 70 comprising dissolved sodium chloride in a concentration of 0.4 to 2% by weight, adding a solution of water glass and acid, uniformly and separately, controlling the dosage by controlling pH ranges ^{from 50} to ⁹⁵ ° C, the value of 7-4, the obtained water and immediately dried, the product, and drying the silica, characterized by the% of final volume, after completion of precipitation and that by the ^straight e ^d lodges u ^d r ^f U is ^runs through at ^d Avan ^as within the range ^{s 3 and} 10, and Te ^p lota in after completion of the addition, the pH of the silica slurry is adjusted to silica is filtered, the resulting filter cake washed with taking care to avoid shear forces on the resultant was the material is sieved through an extruder. 2. The method of claim 1, wherein the volume of the original is at least 50% of the final volume after the precipitation. 3. The method. 2. The process of claim 1, wherein the acid is Si4. Method of extrusion according to sieves. points to 3, characterized in that brushing is used for sieving 5. Method 2 mm. 4. The method of claim 1, wherein a mesh of mesh size 1 to a drawing is used